do not send whole state on action

src/map.ml

@@ -9,10 +9,10 @@ type background =
   | Water
   | Black
 
+type position = int * int * dir
+
 type t =
   { tiles : background array array
-  ; mutable player_pos : int * int
-  ; mutable player_dir : dir
   ; width : int
   ; height : int
   }
@@ -25,23 +25,22 @@ let init () =
         Array.init height (fun _y ->
             if Random.int 1000 <= 42 then Water else Grass ) )
   in
-  { tiles; player_pos = (20, 3); player_dir = Down; width; height }
+  { tiles; width; height }
 
 let get_tile_kind ~x ~y map =
   try map.tiles.(x).(y) with Invalid_argument _ -> Black
 
-let move map dir =
-  if map.player_dir = dir then begin
-    let x, y = map.player_pos in
-    let x, y =
+let check_move map entity_pos dir =
+  let x, y, current_dir = entity_pos in
+  let x, y =
+    if current_dir <> dir then (x, y)
+    else
       match dir with
       | Left -> (x - 1, y)
       | Right -> (x + 1, y)
       | Down -> (x, y + 1)
       | Up -> (x, y - 1)
-    in
-    match get_tile_kind ~x ~y map with
-    | Black | Water -> ()
-    | Grass -> map.player_pos <- (x, y)
-  end
-  else map.player_dir <- dir
+  in
+  match get_tile_kind ~x ~y map with
+  | Black | Water -> Error "invalid terrain"
+  | Grass -> Ok (x, y, dir)